The present invention relates to an axis fixing device and, more particularly, to an axis fixing device for a ratchet wrench. The present invention also relates to a ratchet wrench including the axis fixing device.
U.S. Pat. No. 5,709,136 entitled “POWER DRIVEN TOOLS” discloses a power driven wrench including a head, a drive adapter for a handle, and a rotatable power drive. The head receives a rotatable socket member for connecting to a screw or a bolt. The socket member includes a plurality of gear teeth thereon extending circularly around the socket member and around the axis thereof. The drive adapter includes an outer elongated housing having a central axial bore. Mounted on bearings in the central axial bore is an elongated rotatable drive shaft. A rotary beveled input gear is mounted on the inner end of the drive shaft. The teeth of the rotary beveled input gear mesh with the gear teeth around the socket member for rotation thereof on an axis perpendicular to the axis of the rotation of the drive shaft.
However, during the drilling process for forming the central axial bore of the housing of the power driven wrench, the elongated outline of the housing increases difficulties in bore drilling. Namely, the drilling machine must use a bit with a sufficient length corresponding to the elongated outline of the housing. However, the bending extent of the bit increases when the ratio of the length to the diameter of the bit are larger, such that the bit has to withstand the bending force during the bore drilling process and, thus, flexes, leading to an increase in the error of the bore diameter. After the drilling process, the axis of the central axial bore will inevitably deviate from the axis of the housing. Namely, the central axial bore is defined in the housing along an unideal axis, resulting in an excessive concentricity error between the central axial bore and the housing. Thus, when the drive shaft is mounted in the central axial bore, the rotating axis of the drive shaft will not be perpendicular to the rotating axis of the socket member. As a result, the teeth of the rotary beveled input gear cannot smoothly mesh with the gear teeth of the socket member. The torque of the power drive cannot be transmitted completely through the drive shaft to the socket member. After a long period of use, the rotary beveled input gear and the socket member are subject to damage, and the power driven wrench cannot be used.
Furthermore, the central axial bore must be processed to include a plurality of grooves for receiving the bearings. The problem of concentricity error also exists between the central axial bore and the grooves, such that the drive shaft cannot rotate smoothly in the central axial bore. As a result, the teeth of the rotary beveled input gear cannot smoothly mesh with the gear teeth of the socket member. The torque of the power drive cannot be transmitted completely through the drive shaft to the socket member.
Thus, a need exists for a novel ratchet wrench that mitigates and/or obviates the above disadvantages.